The CS Demonstrator platform was accepted by the end of 2015, being ready for performing tests through the SIS in Real-Time SIS Mode through the GNSS Service Centre. However, the GSC deployment is foreseen by the beginning of 2017, which implied that no tests with real SIS could be performed until then. Due to this limitation, and in order to be able of running tests with real SIS throughout 2016 with which to derive meaningful and realistic conclusions for helping the European Commission with the final definition of the Galileo Commercial Service, the Advanced Replay Mode (ARM) module has been designed and introduced in the experimentation schedule of the AALECS project.
The ARM working mode of the CS Demonstrator has been designed aiming to provide a framework able to support reproducing real user conditions (bit error, occultation, multipath, etc.) without the need of transmitting CS information through the SIS.
For the reproduction of the real environment, the replay capability of the RXP will be used to forward the modified information to the Authentication Client (AC) and PVT Client (PVTC) to evaluate at user level the CS performances, both for the Authentication and High Accuracy Services. This approach overcomes the fact that the current GSC and Galileo infrastructure do not allow yet the transmission of real-time SIS data from the CS Demonstrator, while provide representative results and conclusions for the final performance of the Galileo Commercial Service once the data can be actually transmitted in the SIS.
For the Advanced Replay mode experimentation test the following set up was used : two receivers, a Galileo Commercial Service receiver (RXP) used as rover was placed inside a van and connected to a splitter which was then connected to a common antenna, placed on the roof of the van. In parallel, another RXP unit to be used as reference station was located at GMV’s premises, connected to an antenna place at the top of the roof.
High accuracy tests show that centimeter-level and decimeter-level accuracies can be achieved under open sky conditions with respect to the reference trajectory. However, some degradation in the positioning performances can be observed under urban conditions. This degradation is due to several losses of lines of sight (and therefore the consequent re-convergence of the HA user solution), and not to a degradation in CS data availability.
Several GNSS authentication solutions have been implemented in the frame of the CS Demonstrator project. One of these solution is foreseen to be freely available to all Galileo users as an Open Service Navigation Message Authentication (OS-NMA). This solution is based on a Timed Efficient Stream Loss-Tolerant Authentication (TESLA) scheme. The consortium, together with the EC and GSA, have been working on the definition of OS-NMA.
It can be concluded that the feasibility of a High Accuracy service over the CS signal has been assessed using the 448 bps and 80 bps bandwidths obtaining promising results for a future High Accuracy service to be deployed as part of the Galileo Commercial Service. In addition, experimentation with Open Service Navigation Message Authentication has been performed with a close-to-operational configuration of the authentication solution. The performance of the authenticated positioning solution has shown no significant degradation with respect to standard positioning solutions both in open sky and urban conditions.